Although it is necessary for aerobic respiration, molecular oxygen can be toxic to respiring organisms through its conversion to superoxide, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. The enzyme superoxide dismutase (E.C.1.15.1.1; SOD) appears to provide protection from oxygen radical injury for both plant and animal species. The maize (Zea mays L.) SOD gene-enzyme system has been well characterized genetically, biochemically, and developmentally by our laboratory. This system is well suited for studies concerning the regulation of gene expression during development and may very well serve as a model system with which to gain a better understanding of the mechanisms controlling the sequential activation and stabilization of gene activity in eukaryotes. To continue our characterization of this gene-enzyme system, we plan to develop both cDNA and genomic clones to the various Sod genes in maize. Three alternative methods for producing these clones will help to insure success. Once individual clones are isolated, they will be characterized and sequenced. They will be used initially to identify the primary structure of the Sod genes in maize, intervening sequences, and transcription start and stop sites). Long term uses for the clones involve the analysis of the regulation of expression of the various isozymic forms of SOD during development. This will involve the analysis of transcriptional as well as translational control mechanisms. Towards this end we plan to screen for and identify SOD regulatory mutants which have altered patterns of Sod gene expression during development. One variant of this type has already been identified. We also plan to assess the ability of known free radical-inducing factors to affect SOD levels in maize.